diff --git a/pyproject.toml b/pyproject.toml
index cb9f7fa..d869ed4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "phylm"
-version = "4.0.1"
+version = "4.0.2"
 description = "Phylm"
 authors = ["Dom Batten <dominic.batten@googlemail.com>"]
 license = "MIT"
diff --git a/src/phylm/phylm.py b/src/phylm/phylm.py
index 6db6f67..7124879 100644
--- a/src/phylm/phylm.py
+++ b/src/phylm/phylm.py
@@ -81,15 +81,18 @@ def load_source(self, source: str) -> "Phylm":
             UnrecognizedSourceError: if the source is not recognized
         """
         if source == "imdb":
-            self._imdb = Imdb(raw_title=self.title)
+            if not self._imdb:
+                self._imdb = Imdb(raw_title=self.title)
             return self
 
         if source == "mtc":
-            self._mtc = Mtc(raw_title=self.title)
+            if not self._mtc:
+                self._mtc = Mtc(raw_title=self.title)
             return self
 
         if source == "rt":
-            self._rt = Rt(raw_title=self.title)
+            if not self._rt:
+                self._rt = Rt(raw_title=self.title)
             return self
 
         raise UnrecognizedSourceError(f"{source} is not a recognized source")
diff --git a/tests/unit/test_phylm.py b/tests/unit/test_phylm.py
index 335ea6a..8d7f80a 100644
--- a/tests/unit/test_phylm.py
+++ b/tests/unit/test_phylm.py
@@ -8,6 +8,8 @@
 from phylm.errors import SourceNotLoadedError
 from phylm.errors import UnrecognizedSourceError
 
+MODULE_PATH = "phylm.phylm"
+
 
 class TestInit:
     """Tests for the __init__ method."""
@@ -41,7 +43,7 @@ def test_source_not_found(self) -> None:
         ):
             phylm.load_source("bar")
 
-    @patch("phylm.phylm.Imdb", autospec=True)
+    @patch(f"{MODULE_PATH}.Imdb", autospec=True)
     def test_recognized_source_imdb(self, mock_imdb: MagicMock) -> None:
         """
         Given a `Phylm` instance,
@@ -59,7 +61,7 @@ def test_recognized_source_imdb(self, mock_imdb: MagicMock) -> None:
         assert phylm.imdb == mock_imdb.return_value
         mock_imdb.assert_called_once_with(raw_title="bar")
 
-    @patch("phylm.phylm.Mtc", autospec=True)
+    @patch(f"{MODULE_PATH}.Mtc", autospec=True)
     def test_recognized_source_mtc(self, mock_mtc: MagicMock) -> None:
         """
         Given a `Phylm` instance,
@@ -78,7 +80,7 @@ def test_recognized_source_mtc(self, mock_mtc: MagicMock) -> None:
         assert phylm.mtc == mock_mtc.return_value
         mock_mtc.assert_called_once_with(raw_title="bar")
 
-    @patch("phylm.phylm.Rt", autospec=True)
+    @patch(f"{MODULE_PATH}.Rt", autospec=True)
     def test_recognized_source_rt(self, mock_rt: MagicMock) -> None:
         """
         Given a `Phylm` instance,
@@ -97,12 +99,28 @@ def test_recognized_source_rt(self, mock_rt: MagicMock) -> None:
         assert phylm.rt == mock_rt.return_value
         mock_rt.assert_called_once_with(raw_title="bar")
 
+    @pytest.mark.parametrize("source_class", ("Rt", "Mtc", "Imdb"))
+    def test_source_already_loaded(self, source_class: str) -> None:
+        """
+        Given phylm instance with a source already loaded,
+        When `load_source` is invoked with the same source,
+        Then nothing happens
+        """
+        phylm = Phylm(title="foo")
+
+        with patch(f"{MODULE_PATH}.{source_class}") as mock_source:
+            source_name = source_class.lower()
+            phylm.load_source(source_name)
+            phylm.load_source(source_name)
+
+        assert mock_source.call_count == 1
+
 
 class TestLoadSources:
     """Tests for the `load_sources` method."""
 
-    @patch("phylm.phylm.Mtc", autospec=True)
-    @patch("phylm.phylm.Rt", autospec=True)
+    @patch(f"{MODULE_PATH}.Mtc", autospec=True)
+    @patch(f"{MODULE_PATH}.Rt", autospec=True)
     def test_success(self, mock_rt: MagicMock, mock_mtc: MagicMock) -> None:
         """
         Given a list of sources,
@@ -118,7 +136,7 @@ def test_success(self, mock_rt: MagicMock, mock_mtc: MagicMock) -> None:
         with pytest.raises(SourceNotLoadedError):
             assert phylm.imdb is None
 
-    @patch("phylm.phylm.Rt", autospec=True)
+    @patch(f"{MODULE_PATH}.Rt", autospec=True)
     def test_one_source_not_recognised(self, mock_rt: MagicMock) -> None:
         """
         Given a list of sources where one is unrecognised,